A typical chuck comprises a drive shaft extending along and rotatable about an axis, a housing part adjacent the drive shaft and generally nonrotatable about the axis, and a chuck body fixed to and rotatable with the shaft and formed with a plurality of guides. Respective jaws are shiftable in the guides between closely spaced inner positions and widely spaced outer positions. An adjustment sleeve surrounding the body and coupled to the jaws can be rotated about the axis relative to the body to shift the jaws between their positions.
In the oldest systems, it is standard to form the chuck body adjacent a toothed front edge of the adjustment sleeve with a plurality of radially open pilot holes. A stem of a geared chuck key is inserted in one of the holes and the gear is fitted to the adjustment-sleeve teeth, so that rotation of the key relatively shifts the adjustment sleeve and chuck body. This way considerable torque can be brought to bear both to chuck and dechuck a tool. It is, however, a fairly laborious operation to move the jaws radially between a widely spread and a closely spaced position. Furthermore the chuck key can get lost, and if it is accidentally left in the chuck when the drill is started, it is sent flying and can get lost or injure the user.
In another system the chuck key is dispensed with and the adjustment sleeve is made fairly large so that the user can get a solid grip on it. Either a spindle lock is provided, so that the chuck body can be arrested and the user can manually tighten and loosen the chuck, or the user grips the adjustment sleeve and rotates the chuck body using the drill's motor for chucking and dechucking a tool. Either way the user must exert considerable force, especially with a self-tightening chuck after a drilling operation when the tool can be solidly wedged in place.
EP 0,716,896 describes a system where mechanism is provided to arrest the adjustment sleeve relative to the chuck body. To this end a coupling sleeve is shiftable between a pair of end positions, in one of which the adjustment sleeve is locked to the chuck body and in the other of which it can rotate freely relative to the chuck body. This makes it quite inconvenient when a large-diameter tool is being switch with a small-diameter tool, as the user must hold the tool in place with one hand while manipulating the chuck and operating the drill with the other.